1. Field of the Invention
The present invention relates to a method for detecting a protrusion height of an air bearing surface of a magnetic head slider including a thermally-assisted head.
2. Description of the Related Art
In accordance with higher recording density of hard disk devices, it is desired to diminish a gap between a magnetic head slider and a recording medium. In response to the desire, a magnetic head slider incorporating a heater is proposed as disclosed in JP Laid-Open Patent Publication No. 2003-168274. The heater is disposed near a magnetic recording part and a reproducing part of the magnetic head slider and expands the magnetic head slider by generating heat. Because a relatively wide area of the air bearing surface expands toward the recording medium, the distance from the magnetic recording part and the reproducing part to the recording medium diminishes.
When the distance from the magnetic recording part and the reproducing part to the recording medium is diminished by using the heater disclosed in the above-described publication and when power of the heater (or heater power) is excessively high, thermal expansion of the magnetic head slider becomes excessively large, and thereby the air bearing surface contacts the recording medium. Such contact damages both the recording medium and the magnetic head slider, and therefore the reliability and lifetime of the hard disk device may be degraded. Therefore, it is preferred that the distance from the magnetic recording part and the reproducing part to the recording medium is diminished within the range where the contact of the air bearing surface to the recording medium is preventable. It is known that the distance from the magnetic recording part and the reproducing part to the recording medium can be estimated from, for example, a value of an output voltage of the reproducing part.
On the other hand, for higher recording density of hard disk devices, a magnetic recording system that is called as a thermally-assisted magnetic recording is known. A recording medium that is used for magnetic recording is formed with a non-continuous recording medium made from magnetic microparticles, and each of the magnetic microparticles has a single magnetic domain structure. A recording region (each bit) is formed from a plurality of magnetic microparticles, and thereby boundaries between the recording regions are uneven. In order to increase the recording density, degree of the unevenness should be reduced. In order to achieve this, it is effective to reduce the magnetic microparticles in size; however, a thermal stability is deteriorated associated with a volume reduction of the magnetic microparticles when the magnetic microparticles are reduced in size. In order to enhance the thermal stability, it is preferred to use a magnetic material with a large magnetic anisotropy constant; however, on the other hand, it becomes difficult to record information because coercive force of the recording medium becomes large when anisotropy energy of the magnetic microparticles is increased. Accordingly, in the thermally-assisted magnetic recording, recording to the recording medium is performed in a state where the coercive force is reduced by simultaneously applying a magnetic flux and heat during recording.
U.S. Patent Publication Application No. 2010/0103553 discloses a thermally-assisted head provided with a surface-emitting laser diode and a plasmon generator. Laser light emitting from the laser diode enters into a core configuring a waveguide. The plasmon generator disposed along the core couples in a surface plasmon mode with propagation light propagating through the core at a portion opposing the core to generate surface plasmon. The generated surface plasmon propagates to an end part of the plasmon generator to generate near-field light on the air bearing surface. The coercive force of the recording medium is decreased by heating with the near-field light. In this state, the magnetic flux is supplied from a main pole of a magnetic recording part to the recording medium and thereby information is recorded to the recording medium.
The plasmon generator generates the near-field light in response to the supply of the laser light; however, since its generation efficiency is not 100%, thermal energy that does not contribute to generate the near-field light is partially consumed for heating the plasmon generator itself. As a result, the plasmon generator is heated to a temperature higher than the ambient temperature, causing a large thermal expansion. In a magnetic head slider of a type of thermally-assisted magnetic recording provided with a heater, relatively large range of the air bearing surface is expanded toward the recording medium by the magnetic head slider being thermally-expanded by the heater, and also this large expansion is partially further protruded by the thermal-expansion of the plasmon generator. In the present specification, the relatively large range of the expansion on the air bearing surface is referred to as a first protrusion; and a limited range of a protrusion that is protruded from the first protrusion is referred to as a second protrusion.
In the case of a conventional magnetic head slider provided with no thermally-assisted head, the second protrusion does not occur in principle. Therefore, knowing a protrusion height of the first protrusion or a separation distance between the first protrusion and the recording medium is enough for detecting a separation distance between the magnetic head slider and the recording medium. Because the first protrusion occurs in the relatively large range, the first protrusion can be measured by a conventional technique. On the other hand, in the case of the magnetic head slider of the type of thermally-assisted magnetic recording provided with the heater, the second protrusion that is a portion most protruding on the air bearing surface occurs by the thermal expansion of the plasmon generator, and its range is limited. Therefore, it is impossible to detect with a sufficient accuracy by the conventional technique.
It is objectives of the present invention to provide a method of detecting a protrusion height on the air bearing surface, during operation, of the magnetic head slider including the magnetic recording part of a thermally-assisted type.